I have a web server with more than a few ASP.NET sites running on it. Every so often, i notice that IIS is pushing the server's CPU to 100%. The sites share application pools, per .NET version they are running.

What i'm looking for is a way to be able to pinpoint which site it is that is doing this, using some tool. If that tool happened to get down into the code to show it, that would also be nice. If not, i'm happy just knowing which site is causing the issue.

I've already tried using ANTS. However, with ANTS you need to know which site it is, and then have it running and waiting on said CPU-crashing web app. Not perfectly ideal.

3 Answers
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Some people consider a good practice, create an app pool per website/application, so that when you need to restart a website it will not affect the others.
In the same way, it will create a new IIS worker process w3p.exe per website and by doing so i believe you could monitor more easily each my site was peaking the cpu.

How many App pools? You can start by moving your websites into separate app pools and then using task manager + command line iisapp to match up which app pool matches which task. That will help you identify which web it is to start with.

Failed request tracing in IIS7 can help track down many performance issues with websites, but we still have a broad customer base on IIS6. Troubleshooting performance issues in IIS6 has been quite difficult until Microsoft released a set of tools that gave greater insight into analyzing a stack trace.

The IIS Debug Diagnostics Tool can help track down CPU and memory issues from a worker process. Microsoft has a nice kb article that goes over the basics as well: http://support.microsoft.com/kb/919791.

After a few minutes, a report should be generated containing stack trace information as well as information about any requests executing for longer than 90 seconds. Note that the memory dump with use a few hundred megabytes of space, so be sure to install the tool on a drive with sufficient debugging space. Also, if the box is under heavy load, you can create the user dump on the system, copy the file to your workstation, and perform the analysis locally.